The field of this invention is that of compressing relatively dirty gases in severe service situations involving high pressures and/or high temperatures. Such gases occur when attempting to compress exhaust gases for oil well service operations, such as is described in U.S. Pat. No. 4,811,558 titled System and Method for Providing Compressed Gas.
The above mentioned patent is directed toward compressing diesel engine exhaust gas, however, the improvements in this patent will also apply to the need for compressing other cleaner gases at high temperatures or high pressures.
Historically oilfield service operations have primarily been performed using nitrogen gas. It is an extremely clean gas, but is available only in a cryogenic liquid form (-273 degrees F.) and is expensive to buy, transport, pump, and use. The substantial cost reductions available using exhaust gases for service work make them an attractive alternative.
Uses of exhaust gas taken at ambient pressure directly from the exhaust pipe of an engine provide the capability of using conventional scrubbers to clean the gas, however, the cost of compression of the gas from ambient to 5,000 or 10,000 p.s.i. makes the system as expensive as cryogenic nitrogen. It is as large as a cryogenic nitrogen system.
The patent referred to above draws exhaust gas directly from the cylinder head at 600-800 p.s.i. allowing for much smaller and less expensive secondary compression to higher pressures, but provides a "dirty" gas.